Opening phones
Pry tools kit 21 in 1 - £5.99
https://www.amazon.co.uk/Opening-Repair-Smart-Phone-Disassembly/dp/B01K1X8DYU/
Battery - BLP633
https://www.replacebase.co.uk/for-oneplus-3t-replacement-battery-blp633-3300mah-oem £18.90
https://www.replacebase.co.uk/replacebase-oneplus-3t-replacement-battery-blp633-3-85v-3400mah £19.10
https://www.ifixit.com/Guide/OnePlus+3+Battery+Replacement/119676
https://www.oneplus.com/uk/support/repair-pricing/details?code=6
https://forums.oneplus.com/threads/blp633-or-blp613-battery-for-op3t-europe-a3003-model-128gb-dual-sim.817662/
https://forum.xda-developers.com/oneplus-3t/accessories/replacement-batteries-one-t3794934/amp/
Battery part - BLP637
https://www.oneplus.com/uk/support/repair-pricing/details?code=5
https://www.ifixit.com/Guide/OnePlus+5+Battery+Replacement/103028
https://www.etradesupply.com/oneplus-5-battery-grade-s.html
https://www.replacebase.co.uk/replacebase-oneplus-5-5t-replacement-battery-blp7432-3-5v-3200mah £16.40
https://www.replacebase.co.uk/for-oneplus-5-replacement-battery-blp337-3300mah-oem £10.20
https://www.ebay.co.uk/itm/Internal-Battery-For-OnePlus-5-5T-Phone-BLP637-3300mAh-Replacement-Part-UK/152742215219? £15 free delivery
https://www.amazon.co.uk/OnePlus-Replacement-Battery-BLP337-3300mAh/dp/B076FB5DRF/ £13.80 FREE delivery
https://www.amazon.co.uk/Blue-Star-Premium-Lithium-Compatible/dp/B07XT88XBD/ £20.99 & FREE Delivery
Snapdragon 835
https://www.techwalls.com/qualcomm-snapdragon-835-smartphones/